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Cable/DOCSIS guru question

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Alrighty i have a question.

Is there a proportionate relationship between upload and download speed when dealing with DOCSIS or cable internet, and the reason I ask this is because if there is it seems to be disproportionate to each other.  I understand the idea of pipe capacity and no I not a cable infrastructure guru. 


I carry the following standalone speeds.

Up 70-80 KiloBytes

Down 900-1200 KiloBytes

Spelling it out to avoid confusion.


If my uploads exceed say 15 KB then my downloads are directly effected by a 600-700 KB cut. How does that work? If they total pipe size is somewhere around 1300KB why would an upload limit my download by 600-700KB. 

Possible issues:

Local machine configuration


Comcast configuration


Vista Ult x64

Marvel Yukon 88E8001 Ethernet Controller

Nvidia nforce net controller

Comcast with top tier

Any ideas?

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I'm no guru on the subject either, but I did find a nice clip that could lead you to your answer.

DOCSIS specifies downstream traffic transfer rates between 27 and 36 Mbps over a radio frequency (RF) path in the 50 MHz to 750+ MHz range, and upstream traffic tranfer rates between 320 Kbps and 10 Mbps over a RF path between 5 and 42 MHz. But, because data over cable travels on a shared loop, individuals will see tranfer rates drop as more users gain access.


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huh... that is a really good question.. I don't have the exact technical answer.. but my guess would be that the modem is configured in such a way, through the configuration file that Comcast pushes out, that when you begin to get above 15KB for upload it begin allocating more bandwidth to the upload side of things... The only way to do this would be to pull bandwidth from either bandwidth you are not using or from bandwidth that you are currently using for downloads..  I am sure that there is some type of magic overall bandwidth limit that is set for each individual user/package that prevent you from downloading/uploading at the same time at your max connection speeds.

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That's an excellent question.

It really comes down to mathematics. Too much brain crunching for me to compile, but mudmanc4's quote is very true. This also depends on how many people are on the node, how healthy the mobo cards are in the node per upstream snr levels, time of day (peak/non peak).

This used to be a large issue when cable internet evolved. There was only so much bandwidth to go around, only so many nodes...

Now that the speeds are more than sufficient to handle the media rich websites, the average (non gamer I might add) won't notice or call their local tech support. The only issues now that are being resolved are overcrowded nodes. Once you hit about 600 people on a given node, you can expect some issues.

Cable operators are in the process of thier yearly projects. Upgrading frequencies and also laying more fiber alongside coax to support the load. They'll be called E.O.N. or P.O.N.    E- Meaning Extenable. P- Meaning Passive O.N. Meaning Optical Network. They'll be 'splicing' and 'sweeping' nodes. Some places will double to alleviate crowding. San Diego already has most of thier stuff in place. Any place you can figure they have E.O.D. "On Demand" for cable television, they're ready.

That's a whole nother story.  Hope that strikes interest.

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If my uploads exceed say 15 KB then my downloads are directly effected by a 600-700 KB cut. How does that work? If they total pipe size is somewhere around 1300KB why would an upload limit my download by 600-700KB. 

Maybe a duplex mismatch?

I have never tested my downloads while uploading something at the same time.

There would also be some processor usage issues, but your machine looks pretty quick.

Try the test at http://netspeed.stanford.edu/ and look at the duplex test results.

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Some interesting results maybe.

Normal duplex operation found.

OS data: Name = Windows Vista, Architecture = x86, Version = 6.0

1. Going to have to read up on duplex.

2. I am running an x64 arc.

So I have been digging and digging for the same issue on many many sites.  And I think you are on to something when you talk about the handling of large amounts of packet generation and deconstruction by the CPU.  The dual core AMD is notorious for having this exact issue in servers but my problem is that their is no "cpu driver" for vista x64.  And the only driver for the dual core amd processor is a Microsoft maintained one which is not good because MS is extremely !fast. So any other ideas or comments would be welcomed.

And Keetan, did not mean to ignore your post but I have check my true bandwidth and nod capacity and I am in a newer area and share my node with maybe 50 homes max.  And i have this same disproportionate relationship in peak and off peak. 

Question.  I guess if i really wanted an answer to my question I could dual boot this box with longhorn server/2008 and see what happens then i could officially call it the vista driver problem?

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